Thailand's military rulers will settle down to work at their Bangkok headquarters today, firmly in charge after royal endorsement but facing small protests that so far the security forces have handled with restraint.

Thai coup leader General Prayuth Chan-ocha said on Monday he had been formally endorsed by King Bhumibol Adulyadej as head of a military council in charge of the country. He warned he would use force if protests flared.

Prayuth seized power last week, saying the army had to restore order after nearly seven months of sometimes deadly demonstrations.

The military has detained scores of politicians and activists and anyone defying a summons could be jailed for up to two years. It has censored the media and imposed a nightly curfew.

"We will invite all representatives of all ministries, bureaus and departments such as the national police to meet and discuss work," deputy army spokesperson Srichan Ngathong told reporters, setting out plans after the royal command.

The focus of the military's work is maintaining order and boosting the country's battered economy. Uncertainty has hurt business confidence, halted much government spending and scared away tourists. The economy shrank 2.1 per cent in the first quarter and recession was on the cards.

In the end, the military ousted the elected government of Yingluck Shinawatra. Yingluck's brother is Thaksin Shinawatra, a telecommunications tycoon who became prime minister in 2001 and shook up politics with pro-poor policies.

Accused of corruption and nepotism, Thaksin was ousted in a 2006 coup. He has lived in self-exile since 2008 to avoid a graft conviction he says was politically motivated but he is Thailand's most influential politician and hugely popular among the poor.

He or his party has won every election since 2001 and would probably do so again. The royalist, pro-establishment protesters who took over parts of Bangkok from last November wanted changes to the electoral system and disrupted an election in February that was later annulled.

Prayuth gave no timeframe for a new election in a statement broadcast nationwide on Monday. Thaksin has not commented to the media since the coup but said on Twitter he was saddened.

'GAME OVER'

The junta has based itself at the Royal Thai Army Headquarters, an imposing colonial-style building set back across a lawn on a grand Bangkok avenue.

A few kilometres east is Victory Monument, where protesters have been gathering daily, defying martial law to denounce the coup and call for elections.

Police and soldiers turned out in force on Monday to block several hundred jeering protesters. There were some scuffles but no serious trouble.

Soldiers in a van with a loudspeaker taunted the crowd, saying they were being paid. The soldiers also carped at foreign media, accusing them of trying to damage Thailand.

"The game is over. You can go home now. See you tomorrow," a soldier said over the speakers as the crowd melted into falling darkness.

At nearby Democracy Monument, a small crowd came with posters in support of the army and handed soldiers roses.

Most voters in the capital favour the establishment and approve of the coup if it means getting rid of Thaksin. They believe that as well enriching himself, he was disrespectful to the monarchy. He has denied that.

The crisis between the establishment and Thaksin comes amid anxiety over the issue of royal succession. The king, the world's longest-reigning monarch, is 86 and spent the years from 2009 to 2013 in hospital.

Crown Prince Vajiralongkorn does not command the same devotion as his father, but some Thaksin supporters have recently been expressing their loyalty to the prince.

Some of Thaksin's "red shirt" loyalists, stunned and leaderless since the coup, believe the military will introduce changes to block the Shinawatras from politics once and for all.

An army ranger was killed on Monday in Trat province, near the Cambodian border, in a clash during a raid on suspected pro-Thaksin activists. Authorities seized weapons and detained suspected activists in the northeast late last week.